diff --git a/src/interpreter.rs b/src/interpreter.rs
index 77c082f..324dc77 100644
--- a/src/interpreter.rs
+++ b/src/interpreter.rs
@@ -55,7 +55,7 @@ fn eval_expr_stmt(context: &mut Context, expr: &Expr) -> Result<f64, String> {
 fn eval_expr(context: &mut Context, expr: &Expr) -> Result<f64, String> {
     match expr {
         Expr::Binary(left, op, right) => eval_binary_expr(context, &left, op, &right),
-        Expr::Unary(_, expr) => eval_unary_expr(context, expr),
+        Expr::Unary(op, expr) => eval_unary_expr(context, op, expr),
         Expr::Unit(expr, kind) => eval_unit_expr(context, expr, kind),
         Expr::Var(identifier) => eval_var_expr(context, identifier),
         Expr::Literal(value) => eval_literal_expr(context, value),
@@ -85,8 +85,14 @@ fn eval_binary_expr(
     })
 }
 
-fn eval_unary_expr(context: &mut Context, expr: &Expr) -> Result<f64, String> {
-    eval_expr(context, &expr).clone()
+fn eval_unary_expr(context: &mut Context, op: &TokenKind, expr: &Expr) -> Result<f64, String> {
+    let expr_value = eval_expr(context, &expr)?.clone();
+
+    match op {
+        TokenKind::Minus => Ok(-expr_value),
+        TokenKind::Exclamation => Ok(prelude::funcs::factorial(expr_value)),
+        _ => Err(String::from("Invalid operator for unary expression.")),
+    }
 }
 
 fn eval_unit_expr(context: &mut Context, expr: &Expr, kind: &TokenKind) -> Result<f64, String> {
diff --git a/src/lexer.rs b/src/lexer.rs
index 8e00b93..324bd5b 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -12,6 +12,7 @@ pub enum TokenKind {
     Slash,
     Power,
     Equals,
+    Exclamation,
 
     Deg,
     Rad,
@@ -106,6 +107,10 @@ impl<'a> Lexer<'a> {
                 self.advance();
                 self.build(TokenKind::Equals, "")
             }
+            '!' => {
+                self.advance();
+                self.build(TokenKind::Exclamation, "")
+            }
             ',' => {
                 self.advance();
                 self.build(TokenKind::Comma, "")
diff --git a/src/parser.rs b/src/parser.rs
index 67368be..789de4e 100644
--- a/src/parser.rs
+++ b/src/parser.rs
@@ -30,7 +30,6 @@ pub fn parse(context: &mut Context, input: &str, angle_unit: Unit) -> Result<Opt
     while !is_at_end(context) {
         statements.push(parse_stmt(context)?);
     }
-
     let mut interpreter = interpreter::Context::new(angle_unit, &mut context.symbol_table);
     interpreter.interpret(statements)
 }
@@ -147,7 +146,7 @@ fn parse_unary(context: &mut Context) -> Result<Expr, String> {
 }
 
 fn parse_exponent(context: &mut Context) -> Result<Expr, String> {
-    let left = parse_primary(context)?;
+    let left = parse_factorial(context)?;
 
     if match_token(context, TokenKind::Power) {
         let op = advance(context).kind.clone();
@@ -158,6 +157,17 @@ fn parse_exponent(context: &mut Context) -> Result<Expr, String> {
     Ok(left)
 }
 
+fn parse_factorial(context: &mut Context) -> Result<Expr, String> {
+    let expr = parse_primary(context)?;
+
+    Ok(if match_token(context, TokenKind::Exclamation) {
+        advance(context);
+        Expr::Unary(TokenKind::Exclamation, Box::new(expr))
+    } else {
+        expr
+    })
+}
+
 fn parse_primary(context: &mut Context) -> Result<Expr, String> {
     let expr = match peek(context).kind {
         TokenKind::OpenParenthesis => parse_group(context)?,
diff --git a/src/prelude.rs b/src/prelude.rs
index be915a6..fd3b6fa 100644
--- a/src/prelude.rs
+++ b/src/prelude.rs
@@ -56,6 +56,7 @@ pub const BINARY_FUNCS: phf::Map<&'static str, BinaryFuncInfo> = phf::phf_map! {
     "min" => BinaryFuncInfo(min, Other),
     "hyp" => BinaryFuncInfo(hyp, Other),
     "log" => BinaryFuncInfo(logx, Other),
+    "sqrt" => BinaryFuncInfo(nth_sqrt, Other),
 };
 
 enum FuncType {
@@ -124,7 +125,7 @@ fn from_angle_unit(x: f64, angle_unit: &Unit) -> f64 {
     }
 }
 
-mod funcs {
+pub mod funcs {
     pub fn abs(x: f64) -> f64 {
         x.abs()
     }
@@ -212,6 +213,15 @@ mod funcs {
         x.exp()
     }
 
+    pub fn factorial(x: f64) -> f64 {
+        let mut value = 1;
+        for i in 1..=x as i32 {
+            value *= i;
+        }
+
+        value as f64
+    }
+
     pub fn floor(x: f64) -> f64 {
         x.floor()
     }
@@ -268,6 +278,10 @@ mod funcs {
         x.sqrt()
     }
 
+    pub fn nth_sqrt(x: f64, n: f64) -> f64 {
+        x.powf(1f64 / n)
+    }
+
     pub fn tan(x: f64) -> f64 {
         x.tan()
     }